Idz
03-21-2015, 02:07 PM
It is a lot of fun to start with a CBC 24 ga case and form it into a MH. The Lee dies required a lot of force so I decided to try to make my own dies.
134631 134632 134633
I made these dies out of 7/8-14 threaded rod so they fit a standard press. My finish dies I made in two pieces so I could separate them to reduce the forces needed.
134634
Here's the stages of forming. The left is a raw CBC 24 ga case, then trimmed to 2.28", next I form a cone, then anneal the shoulder and form the neck, finally anneal the shoulder and the two piece die forms the case taper and shoulder. I form a bit of case, back off and rotate the case, then form a bit more. About 3-4 strokes per step. I anneal using the finger technique of hold the base in my fingers and rotating it in a propane torch flame about 10 seconds until its too hot to hold and then drop it into water.
For the science geeks: The yield strength of hard cartridge brass is 60000 psi and 17000psi annealed, mild steel is about 40000psi. So to form hard brass with a 0.012" wall requires about 1440 lbs/linear inch of die. Using just the die thread root diameter and assuming a 0.650 ID the stress in the die is 18701 psi so the 7/8-14 rod has no problem. Now using a Young's modulus of 29,000,000 psi we can calculate the die diameter increase under the stress is about 0.0005", again no problem.
Overall a fun project.
134631 134632 134633
I made these dies out of 7/8-14 threaded rod so they fit a standard press. My finish dies I made in two pieces so I could separate them to reduce the forces needed.
134634
Here's the stages of forming. The left is a raw CBC 24 ga case, then trimmed to 2.28", next I form a cone, then anneal the shoulder and form the neck, finally anneal the shoulder and the two piece die forms the case taper and shoulder. I form a bit of case, back off and rotate the case, then form a bit more. About 3-4 strokes per step. I anneal using the finger technique of hold the base in my fingers and rotating it in a propane torch flame about 10 seconds until its too hot to hold and then drop it into water.
For the science geeks: The yield strength of hard cartridge brass is 60000 psi and 17000psi annealed, mild steel is about 40000psi. So to form hard brass with a 0.012" wall requires about 1440 lbs/linear inch of die. Using just the die thread root diameter and assuming a 0.650 ID the stress in the die is 18701 psi so the 7/8-14 rod has no problem. Now using a Young's modulus of 29,000,000 psi we can calculate the die diameter increase under the stress is about 0.0005", again no problem.
Overall a fun project.